This invention relates to systems and methods for processing blood, e.g., for filtration, pheresis, or other diagnostic or therapeutic purposes.
There are many types of continuous and intermittent blood processing systems, each providing different therapeutic effects and demanding different processing criteria.
For example, hemofiltration emulates normal kidney activities for an individual whose renal function is impaired or lacking. During hemofiltration, blood from the individual is conveyed in an extracorporeal path along a semipermeable membrane, across which a pressure difference (called transmembrane pressure) exists. The pores of the membrane have a molecular weight cut-off that can thereby pass liquid and uremic toxins carried in blood. However, the membrane pores can not pass formed cellular blood elements and plasma proteins. These components are retained and returned to the individual with the toxin-depleted blood. Membranes indicated for hemofiltration are commercially available and can be acquired from, e.g., Asahi Medical Co. (Oita, Japan).
After hemofiltration, fresh physiologic fluid is supplied to toxin-depleted blood. This fluid, called replacement fluid, is buffered either with bicarbonate, lactate, or acetate. The replacement fluid restores, at least partially, a normal physiologic fluid and electrolytic balance to the blood. Usually, an ultrafiltration function is also performed during hemofiltration, by which liquid is replaced in an amount slightly less than that removed. Ultrafiltration decreases the overall fluid level of the individual, which typically increases, in the absence of ultrafiltration, due to normal fluid intake between treatment sessions.
Following hemofiltration, fluid balancing, and ultrafiltration, the blood is returned to the individual.
The invention provides fluid replacement systems and methods for association with a hemofilter, which removes waste fluid from blood. The systems and methods convey an individual""s blood through an extracorporeal fluid circuit to the hemofilter to remove waste fluid. The systems and methods convey waste fluid from the hemofilter through a waste line.
The systems and methods operate in a first cycle to convey waste fluid in the waste line into a first compartment of a chamber. The chamber includes an interior wall dividing the chamber into the first compartment to retain a volume of the waste fluid and a second compartment to retain a volume of replacement fluid. The interior wall responds to differential fluid pressure to displace replacement fluid from the second compartment into a return line to the individual as waste fluid is conveyed into the first compartment.
The systems and methods operate in a second cycle to convey replacement fluid into the second compartment. The interior wall responds to differential fluid pressure to displace waste fluid from the first compartment into a drain line as replacement fluid is conveyed into the second compartment.
According to one aspect of the invention, the systems and methods selectively operate in a bolus mode during the first and second cycles. During the bolus mode, a volume of waste fluid is recirculated from the first compartment into the waste line. The systems and methods thereby limit removal of additional waste fluid by the hemofilter, while displacing replacement fluid from the second compartment into the return line.
According to another aspect of the invention, the systems and methods convey blood from the hemofilter through a blood return line after removal of waste fluid. The systems and methods operate, in the first cycle, to displace replacement fluid from the second compartment into the blood return line for mixing with blood as waste fluid is conveyed into the first compartment. The systems and methods operate, during the second cycle, to displace waste fluid from the first compartment into a drain line as replacement fluid is conveyed into the second compartment. According to this aspect of the invention, the systems and methods selectively operate in a rinse back mode, during which a volume of waste fluid is recirculated from the first compartment into the waste line to displace replacement fluid from the second compartment into the blood return line while blood flow through the return line is terminated. The systems and methods thereby flush the blood return line with replacement fluid.